Transient global amnesia is a sudden, temporary episode of memory loss that can't be attributed to a more common neurological condition, such as epilepsy or stroke.

During an episode of transient global amnesia, your recall of recent events simply vanishes, so you can't remember where you are or how you got there. In addition, you may not remember anything about what's happening in the here and now. Consequently, you may keep repeating the same questions because you don't remember the answers you've just been given. You may also draw a blank when asked to remember things that happened a day, a month or even a year ago.

With transient global amnesia, you do remember who you are, and recognize the people you know well. But that doesn't make your memory loss less disturbing.

Fortunately, transient global amnesia is rare, seemingly harmless and unlikely to happen again. Episodes are usually short-lived, and afterward your memory is fine.

Transient global amnesia is identified by its main symptom, which is the inability to form new memories and to recall the recent past. Once that symptom is confirmed, ruling out other possible causes of amnesia is important.

Necessary symptoms for diagnosis

Health care professionals base a diagnosis of transient global amnesia on the following signs and symptoms:

Sudden onset of memory loss, verified by a witness

Retention of personal identity despite memory loss

Normal cognition, such as the ability to recognize and name familiar objects and follow simple directions

Absence of signs indicating damage to a particular area of the brain, such as limb paralysis, involuntary movement or impaired word recognition

Additional symptoms and history on which a diagnosis for transient global amnesia is based:

Duration of no more than 24 hours and generally shorter

Gradual return of memory

No evidence of seizures during the period of amnesia

No history of active epilepsy

Along with these signs and symptoms, a common feature of transient global amnesia includes repetitive questioning, usually of the same question — for example, "What am I doing here?" or "How did we get here?"

When to see a doctor

Seek immediate medical attention for anyone who quickly goes from normal awareness of present reality to confusion about what just happened. If the person experiencing memory loss is too disoriented to call an ambulance, call one yourself.

Although transient global amnesia isn't harmful, there's no easy way to distinguish the condition from the life-threatening illnesses that can also cause sudden memory loss. In fact, sudden amnesia is much more likely to be caused by a stroke or a seizure than by transient global amnesia. A medical evaluation is the only way to determine the cause of sudden memory loss.

The underlying cause of transient global amnesia is unknown. There appears to be a link between transient global amnesia and a history of migraines, though the underlying factors that contribute to both conditions aren't fully understood.

Acute emotional distress, as might be provoked by bad news, conflict or overwork

Interestingly, high blood pressure and high cholesterol — which are closely linked to strokes — are not risk factors for transient global amnesia. Your sex doesn't seem to affect your risk, either.

The clearest risk factors are:

Age. People age 50 and older have a higher risk of transient global amnesia than do younger people.

History of migraines. If you have migraines, your risk of transient global amnesia is significantly higher than that of someone without migraines.

Transient global amnesia has no direct complications, but it can cause emotional distress. If you have an episode, the gap in your memory can be unsettling, and you're likely to worry about a recurrence.

Also, a symptom as dramatic as memory loss often indicates a serious underlying disease. Transient global amnesia is an exception, but it can be hard to let go of the fear that you have a tumor or had a stroke.

If you need reassurance, ask your doctor to go over the results of your neurological exam and diagnostic tests with you. A counselor or psychotherapist can help you deal with persistent anxiety. Importantly, transient global amnesia is not a risk factor for stroke.

Anyone who experiences sudden loss of memory for all events leading up to the present needs emergency medical care. Call 911 or your local emergency number immediately.

If a friend or family member develops these symptoms in your presence, go with him or her to the hospital. Because he or she doesn't remember recent events, you'll need to provide important information to the doctor.

What you can do

Stay with the person through the full medical evaluation. Sudden memory loss may indicate a serious health problem. Take an active role in noting all the information the doctor provides and in helping to make decisions about next steps.

Share with medical staff physically or emotionally stressful events that preceded the memory loss. Important details include conflict or anxiety at work or at home, strenuous physical activity, sudden immersion in hot or cold water — anything that may have caused the person alarm or strain.

Note any accompanying signs or symptoms, such as numbness, weakness or trembling.

Relay key medical information, including any other conditions with which the person has been diagnosed. Also include all medications he or she is taking.

Write down questions to ask the doctor.

Prepare a list of questions to ask the doctor on the person's behalf. Although people experiencing transient global amnesia can think and speak, it's likely that they will be feeling severe distress. For transient global amnesia, some basic questions include:

What is most likely causing the symptoms?

What are the other possible causes for these symptoms?

What kinds of tests do you recommend?

Is any treatment needed now?

What signs or symptoms should I be watching for at home?

What signs or symptoms should prompt calling 911 or emergency medical help?

How soon do you expect the symptoms to improve?

Do you expect a full recovery?

Are there any steps to take to prevent a recurrence of this problem?

What is the risk of long-term complications from this condition?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions as they occur to you during the appointment.

What to expect from your doctor

The doctor is likely to ask both you and the person experiencing amnesia a number of questions about symptoms and about the period leading up to the memory loss.

The doctor may ask your loved one:

What is the last thing you remember?

Do you know who you are?

Do you know the person who came with you?

Do you have any symptoms other than memory loss?

Are you dizzy?

Are you having problems with balance or coordination?

Do you feel weakness or numbness on either side of your body?

Are you having any vision problems?

Do your symptoms include headache?

To determine the extent of memory loss, the doctor may check your loved one's knowledge of general information — such as the name of the current president — and assess his or her ability to recall a random list of words.

The doctor may ask you:

When did the person's memory loss begin?

Did the memory loss come on gradually or suddenly?

Has anything like this ever happened before?

What happened just before the memory loss?

Did the person experience an accident that may have injured his or her head?

Has the person recently experienced significant stress, conflict or loss?

Has he or she had a seizure since symptoms began?

Has the person been diagnosed with any other medical conditions?

Does he or she have a history of migraines?

Has the person recently undergone any medical procedures or surgery?

What medications is he or she taking, including prescription drugs, over-the-counter medications, herbs and supplements?

Diagnosis of transient global amnesia rests on excluding more-serious conditions — stroke, seizure or head injury, for example — that can cause the same type of memory loss.

Brain and imaging tests

The next step is to conduct tests that detect abnormalities in the brain's electrical activity and circulation. The most common of these tests are painless and take less than two hours each:

Magnetic resonance imaging (MRI). This technique uses a magnetic field and radio waves to create detailed, cross-sectional images of the brain. The MRI machine can combine these slices to produce 3-D images that may be viewed from many different angles.

Electroencephalogram (EEG). An EEG records the brain's electrical activity via electrodes attached to the scalp. People with epilepsy often have changes in their brain waves, even when they're not having a seizure.

Computerized tomography (CT). Using special X-ray equipment, your doctor obtains images from many different angles and joins them together to show cross-sectional images of the brain and skull. CT scans can reveal abnormalities in brain structure, including narrowed, overstretched or broken blood vessels and past strokes.

No treatment is needed for transient global amnesia. It resolves on its own and has no confirmed aftereffects.

Because the cause of transient global amnesia is unknown and the rate of recurrence is low, no standard approaches for preventing the condition exist. If your episode of transient global amnesia followed a particular activity, such as a strenuous workout or a swim in a chilly lake, talk with your doctor about limiting or avoiding the activity that seemed to trigger your memory loss.

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